With global warming becoming an increasingly serious issue worldwide, the development of environmentally friendly refrigeration and air-conditioning systems has become increasingly important. In addition to having an impact on global warming, refrigerants are greatly involved in the performance of refrigeration and air-conditioning systems. Therefore, refrigerant selection has an important role in reducing carbon dioxide emissions that contribute to global warming.
Recently, a variety of partially fluorinated propenes having a double bond in the molecule have been proposed. Such propenes have a lower global warming potential (GWP) compared with known chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), and hydrofluorocarbon (HFC).
2,3,3,3-Tetrafluoropropene (HFO1234yf) is one such propene (see, for example, Patent Literatures 1 and 2). This refrigerant is flammable, and ignites at a concentration of 6.5 to 12.5 vol. % in air at 21° C. In addition, this refrigerant has a higher boiling point than HCFC22, which has been conventionally used in stationary air conditioners, and R407c and R410A, which have come into use as alternatives to HCFC22 and are uninvolved in the depletion of the ozone layer. For this reason, the refrigerating capacity cannot be maintained by the use of HFO1234yf alone.
In the selection of a refrigerant, a low global warming potential (GWP) of the refrigerant itself is obviously important; however, the energy use efficiency of the device using the refrigerant is equally, or more important. The former is evaluated as a direct environmental impact, and the latter as an indirect environmental impact. LCCP (Life Cycle Climate Performance) has been proposed as an objective index for these evaluations (Non-Patent Literature 1 etc.). Although LCCP is now widely recognized for use in the comprehensive evaluation of refrigerants, there have been no cases where LCCP evaluation has been performed to provide optimal refrigerants.